The research outlined in this application is carried out with the objective of obtaining basic information which can be used to build an understanding in molecular terms of physiologically important phenomena associated with biological membranes. Work is centered on the continuing investigation of the interactions between lipids in multicomponent bilayers and the relations between these interactions and the properties and molecular structure of multicomponent systems. Of special interest are multicomponent bilayers exhibiting compositional domain structure either within the plane of the bilayer or within its apposing faces. Emphasis is placed on bilayers containing primary amine phospholipids, sphingomyelins or glycosphingolipids since many of these substances in pure systems have been shown, or may be expected to have gel-liquid crystalline phase transition in the region of 37 degrees Centigrade. The bilayer systems employed in this study are primarily liposome dispersions of the multilamellar and small single-lamellar vesicle types. Limited use is also made of planar and spherical Mueller-Rudin systems and monolayer studies at an air/water interface. The biological membranes studied will be confined to vesicular stomatitis virus and its close relatives and to the bovine rod outer segment discs. Assessment of the parameters describing interactions betweeen the lipid components of these bilayer systems will depend upon a variety of physical techniques including the use of fluorescent probes, NMR spectroscopy (proton, 13C and 31P), scanning calorimetry, partial molal volume measurement, and the use of hydrodynamic methods to characterize membrane and bilayer vesicle dispersions.